This invention relates generally to belt driven machines, and in particular to a combined pulley and belt locator which transmits power to a drive belt and maintains the belt at a proper operating position.
Many appliances have an endless belt which transmits power and motion from a motor to a driven component. For example, an automatic clothes dryer has an electric motor which drives a flexible belt to rotate a drum containing wet clothing. A pulley is mounted along an end of a motor drive shaft and rotates with the shaft for moving the belt. The pulley typically is threaded onto a corresponding threaded portion of the shaft. The belt engages the pulley and is aligned with a belt-driving section of the pulley. A blower is also attached to the drive shaft for circulating air through the dryer to remove moisture from the clothing as it tumbles in the drum.
Unfortunately, the motor is frequently located in a dryer housing at a position which is not easily accessible nor in view. A person performing initial assembly of the dryer or subsequent maintenance must install the belt “blindly,” without seeing the pulley. As a result, the belt may inadvertently be misaligned, or be installed around the shaft instead of the pulley. That produces improper belt tensions and uncertain speed ratios which reduce the life of the belt and lead to operational failure. To avoid these difficulties, a belt restrainer has frequently been installed on the shaft adjacent to the pulley. The belt restrainer, or belt guide, is typically a plastic shroud having an external surface sloping toward the pulley which, when rotated, causes a misplaced belt engaging the surface to move to its proper position on the pulley. The belt guide has an internal collar for mounting on the drive shaft and a series of internal ribs which support the structure of the shroud. An example of such a belt guide is described in U.S. Pat. No. 4,929,219, issued May 29, 1990 and entitled “Belt Locator For Locating A Belt On A Pulley.”
The belt guide can lead to additional expense and delay. Workers occasionally forget to install a belt guide, or install it on the drive shaft in a backwards orientation with the surface sloping away from the pulley. A maintenance action is then required to remove the pulley from the shaft and properly install the belt guide. The plastic material of the belt guide can be less durable than other surrounding parts which are metallic. Moreover, the production costs associated for molding the plastic guide adds to the substantial costs already required for machining the pulley.
Production of the pulley can also be relatively inefficient. It is made from a solid piece of steel which is machined to define the complex geometry and to eliminate any sharp edges which could damage or destroy the belt. Pulleys have not typically been made by a die casting process because molded parts often exhibit discontinuities in surface contours (referred to as “parting lines”) forming sharp edges which rapidly abrade the belt and lead to premature failure.
An additional shortcoming is that the pulley cannot be used for holding the drive shaft at a fixed position. To install or remove the blower from the drive shaft, the shaft must be held stationary while the blower is rotated for tightening or loosening its threaded connection. Because the pulley is threaded onto that shaft, it may not be used as a grip for preventing rotation of the shaft because its own threaded connection would be affected. Instead, a flat surface or a slot is typically machined into the shaft to facilitate holding the shaft with a tool. Unfortunately, the machining of the shaft degrades the strength and life of the shaft, increases manufacturing time, and limits the types of suitable materials for making the shaft.